Acetylcholinesterase accelerates assembly of amyloid-beta-peptides into Alzheimer's fibrils: possible role of the peripheral site of the enzyme

Acetylcholinesterase (AChE), an important component of cholinergic synapses, colocalizes with amyloid-beta peptide (A beta) deposits of Alzheimer's brain. We report here that bovine brain AChE, as well as the human and mouse recombinant enzyme, accelerates amyloid formation from wild-type A beta and a mutant A beta peptide, which alone produces few amyloid-like fibrils. The action of AChE was independent of the subunit array of the enzyme, was not affected by edrophonium, an active site inhibitor, but it was affected by propidium, a peripheral anionic binding site ligand. Butyrylcholinesterase, an enzyme that lacks the peripheral site, did not affect amyloid formation. Furthermore, AChE is a potent amyloid-promoting factor when compared with other A beta-associated proteins. Thus, in addition to its role in cholinergic synapses, AChE may function by accelerating A beta formation and could play a role during amyloid deposition in Alzheimer's brain.

Apolipoprotein E immunoreactivity in cerebral amyloid deposits and neurofibrillary tangles in Alzheimer's disease and kuru plaque amyloid in Creutzfeldt-Jakob disease

During the course of our immunohistochemical studies on the change of lipids in Alzheimer's disease brains by using antibody to apolipoprotein E, a protein having a special relevance to nervous tissue, we unexpectedly found that apo E immunoreactivity was associated with amyloid in both senile plaques and cerebral vessels and neurofibrillary tangles. The immunoreactivity was also found in amyloid of kuru plaques in Creutzfeldt-Jakob disease. Pretreatment of the sections with formic acid greatly enhanced immunoreactivity of senile and kuru plaques to antibody to apo E.

Assembly of microtubule-associated protein tau into Alzheimer-like filaments induced by sulphated glycosaminoglycans

The paired helical filament (PHF) is the major component of the neurofibrillary deposits that form a defining neuropathological characteristic of Alzheimer's disease. PHFs are composed of microtubule-associated protein tau, in a hyperphosphorylated state. Hyperphosphorylation of tau results in its inability to bind to microtubules and is believed to precede PHF assembly. However, it is unclear whether hyperphosphorylation of tau is either necessary or sufficient for PHF formation. Here we show that non-phosphorylated recombinant tau isoforms with three microtubule-binding repeats form paired helical-like filaments under physiological conditions in vitro, when incubated with sulphated glycosaminoglycans such as heparin or heparan sulphate. Furthermore, heparin prevents tau from binding to microtubules and promotes microtubule disassembly. Finally, we show that heparan sulphate and hyperphosphorylated tau coexist in nerve cells of the Alzheimer's disease brain at the earliest known stages of neurofibrillary pathology. These findings, with previous studies which show that heparin stimulates tau phosphorylation by a number of protein kinases, indicate that sulphated glycosaminoglycans may be a key factor in the formation of the neurofibrillary lesions of Alzheimer's disease.

The slow component of axonal transport. Identification of major structural polypeptides of the axon and their generality among mammalian neurons

This study of the slow component of axonal transport was aimed at two problems: the specific identification of polypeptides transported into the axon from the cell body, and the identification of structural polypeptides of the axoplasm. The axonal transport paradigm was used to obtain radioactively labeled axonal polypeptides in the rat ventral motor neuron and the cat spinal ganglion sensory neuron. Comparison of the slow component polypeptides from these two sources using sodium dodecyl sulfate (SDS)-polyacrylamide electrophoresis revealed that they are identical. In both cases five polypeptides account for more than 75% of the total radioactivity present in the slow component. Two of these polypeptides have been tentatively identified as tubulin, the microtubule protein, on the basis of their molecular weights. The three remaining polypeptides with molecular weights of 212,000, 160,000, and 68,000 daltons are constitutive, and as such appear to be associated with a single structure which has been tentatively identified as the 10-nm neurofilament. The 212,000-dalton polypeptide was found to comigrate in SDS gels with the heavy chain of chick muscle myosin. The demonstration on SDS gels that the slow component is composed of a small number of polypeptides which have identical molecular weights in neurons from different mammalian species suggests that these polypeptides comprise fundamental structures of vertebrate neurons.

Tau pathology in Alzheimer disease and other tauopathies

Just as neuronal activity is essential to normal brain function, microtubule-associated protein tau appears to be critical to normal neuronal activity in the mammalian brain, especially in the evolutionary most advanced species, the homo sapiens. While the loss of functional tau can be compensated by the other two neuronal microtubule-associated proteins, MAP1A/MAP1B and MAP2, it is the dysfunctional, i.e., the toxic tau, which forces an affected neuron in a long and losing battle resulting in a slow but progressive retrograde neurodegeneration. It is this pathology which is characteristic of Alzheimer disease (AD) and other tauopathies. To date, the most established and the most compelling cause of dysfunctional tau in AD and other tauopathies is the abnormal hyperphosphorylation of tau. The abnormal hyperphosphorylation not only results in the loss of tau function of promoting assembly and stabilizing microtubules but also in a gain of a toxic function whereby the pathological tau sequesters normal tau, MAP1A/MAP1B and MAP2, and causes inhibition and disruption of microtubules. This toxic gain of function of the pathological tau appears to be solely due to its abnormal hyperphosphorylation because dephosphorylation converts it functionally into a normal-like state. The affected neurons battle the toxic tau both by continually synthesizing new normal tau and as well as by packaging the abnormally hyperphosphorylated tau into inert polymers, i.e., neurofibrillary tangles of paired helical filaments, twisted ribbons and straight filaments. Slowly but progressively, the affected neurons undergo a retrograde degeneration. The hyperphosphorylation of tau results both from an imbalance between the activities of tau kinases and tau phosphatases and as well as changes in tau's conformation which affect its interaction with these enzymes. A decrease in the activity of protein phosphatase-2A (PP-2A) in AD brain and certain missense mutations seen in frontotemporal dementia promotes the abnormal hyperphosphorylation of tau. Inhibition of this tau abnormality is one of the most promising therapeutic approaches to AD and other tauopathies.

The growth inhibitory factor that is deficient in the Alzheimer's disease brain is a 68 amino acid metallothionein-like protein

We have purified and characterized the growth inhibitory factor (GIF) that is abundant in the normal human brain, but greatly reduced in the Alzheimer's disease (AD) brain. GIF inhibited survival and neurite formation of cortical neurons in vitro. Purified GIF is a 68 amino acid small protein, and its amino acid sequence is 70% identical to that of human metallothionein II with a 1 amino acid insert and a unique 6 amino acid insert in the NH2-terminal and the COOH-terminal portions, respectively. The antibodies to the unique sequence of GIF revealed a distinct subset of astrocytes in the gray matter that appears to be closely associated with neuronal perikarya and dendrites. In the AD cortex, the number of GIF-positive astrocytes was drastically reduced, suggesting that GIF is down-regulated in the subset of astrocytes during AD.

Intraneuronal aluminum accumulation in amyotrophic lateral sclerosis and Parkinsonism-dementia of Guam

Scanning electron microscopy with energy-dispersive x-ray spectrometry was used to analyze the elemental content of neurofibrillary tangle (NFT)-bearing and NFT-free neurons within the Sommer's sector (H1 region) of the hippocampus in Guamanian Chamorros with amyotrophic lateral sclerosis and parkinsonism-dementia and in neurologically normal controls. Preliminary data indicate prominent accumulation of aluminum within the nuclear region and perikaryal cytoplasm of NFT-bearing hippocampal neurons, regardless of the underlying neurological diagnosis. These findings further extend the association between intraneuronal aluminum and NFT formation and support the hypothesis that environmental factors are related to the neurodegenerative changes seen in the Chamorro population.

Proline-directed and non-proline-directed phosphorylation of PHF-tau

To gain insight into the abnormal phosphorylation of PHF-tau, we have determined the phosphorylation sites by identifying phosphopeptides by means of ion spray mass spectrometry followed by sequencing of ethane-thiol-modified peptides. Nineteen sites have been identified; all but Ser-262 are localized to the amino- and carboxyl-terminal flanking regions of the microtubule-binding domain. Eleven sites correspond to fetal type sites. Unexpectedly, 10 are non-proline-directed, whereas the others are proline-directed. Thus, the abnormal phosphorylation of PHF-tau can be considered to consist of fetal type phosphorylation and additional proline-directed and non-proline-directed phosphorylation. This non-fetal type phosphorylation may provide PHF-tau with the unusual characteristics.

beta-amyloid fibrils induce tau phosphorylation and loss of microtubule binding

A central issue in the pathogenesis of Alzheimer's disease (AD) is the relationship between amyloid deposition and neurofibrillary tangle formation. To determine whether amyloid fibril formation affects the phosphorylation state of tau, primary cultures of fetal rat hippocampal and human cortical neurons were treated with beta-amyloid (beta A) in a soluble, amorphous-aggregated, or fibrillar form. Fibrillar beta A, but not soluble or amorphous-aggregated beta A, markedly induces the phosphorylation of tau at Ser-202 and Ser-396/Ser-404, resulting in a shift in the tau M(r) in human cortical neurons. Hyperphosphorylated tau accumulates in the somatodendritic compartment of fibrillar beta A-treated neurons in a soluble form that is not associated with microtubules and is incapable of binding to microtubules in vitro. Dephosphorylation of beta A-induced tau restores its capacity to bind to microtubules. Thus, amyloid fibril formation alters the phosphorylation state of tau, resulting in the loss of microtubule binding capacity and somatodendritic accumulation, properties also exhibited by tau in the AD brain. Amyloid fibril formation may therefore be a cause of abnormal tau phosphorylation in AD.

Cytoplasmic penetration and persistent infection of mammalian cells by polyglutamine aggregates

Sequence-specific nucleated protein aggregation is closely linked to the pathogenesis of most neurodegenerative diseases and constitutes the molecular basis of prion formation. Here we report that fibrillar polyglutamine peptide aggregates can be internalized by mammalian cells in culture where they gain access to the cytosolic compartment and become co-sequestered in aggresomes together with components of the ubiquitin-proteasome system and cytoplasmic chaperones. Remarkably, these internalized fibrillar aggregates are able to selectively recruit soluble cytoplasmic proteins with which they share homologous but not heterologous amyloidogenic sequences, and to confer a heritable phenotype on cells expressing the homologous amyloidogenic protein from a chromosomal locus.

Slow axonal transport of neurofilament proteins: impairment of beta,beta'-iminodipropionitrile administration

beta,beta'-Iminodipropionitrile (IDPN) administration prevented normal slow axonal transport of [35S]methionine- or [3H]leucine-labeled proteins in rat sciatic motor axons. Ultrastructural and electrophoretic studies showed that the neurofilament triplet proteins in particular were retained within the initial 5 millimeters of the axons, resulting in neurofilament-filled axonal swellings. Fast anterograde and retrograde axonal transport were not affected. The IDPN thus selectively impaired slow axonal transport. The neurofibrillary pathology in this model is the result of the defective slow transport of neurofilaments.

Oxidative stress precedes fibrillar deposition of Alzheimer's disease amyloid beta-peptide (1-42) in a transgenic Caenorhabditis elegans model

Alzheimer's disease is a progressive, neurodegenerative disorder characterized by senile plaques and neurofibrillary components. Abeta(1-42) is a principal component of senile plaques and is thought to be central to the pathogenesis of the disease. The Alzheimer's disease brain is under significant oxidative stress, and the Abeta(1-42) peptide is known to cause oxidative stress in vitro. One controversy in the amyloid hypothesis is whether or not Abeta plaques are required for toxicity. We have employed a temperature-inducible Abeta expression system in Caenorhabditis elegans to create a strain of worms, CL4176, in which Abeta(1-42) is expressed with a non-permissive temperature of 23 degrees C. The CL4176 strain allows examination of the temporal relationship between Abeta expression, oxidative stress, and Abeta fibril formation. CL4176 were under increased oxidative stress, evidenced by increased protein oxidation indexed by increased carbonyl levels, 24 and 32 h after temperature upshift as compared to the control strain, CL1175. The increased oxidative stress in CL4176 occurred in the absence of Abeta fibril formation, consistent with the notion that the toxic species in Abeta toxicity is pre-fibrillar Abeta and not the Abeta fibril. These results are discussed with reference to Alzheimer's disease.

Massive somatodendritic sprouting of cortical neurons in Alzheimer's disease

In addition to neurofibrillary tangles and senile plaques, antibodies to human tau revealed extensive tau-immunoreactive meshworks in layers III and V of the neocortex affected with Alzheimer's disease. The meshworks consisted of innumerable abnormally curly fibers, which were coming from somata and dendrites of pyramidal cells. Their morphological appearance suggests that those curly fibers represent somatodendritic sprouting.

The vimentin-GFA protein transition in rat neuroglia cytoskeleton occurs at the time of myelination

Extraction with Triton, a nonionic detergent, is a common procedure to prepare intermediate filament enriched fractions from cells maintained in culture. The Triton-Insoluble fraction is called a cytoskeletal preparation. Using this procedure, we previously demonstrated that vimentin and glial fibrillary acidic protein (GFA) are major cytoskeletal proteins of neuroglia, in newborn and adult rat brain, respectively. In the present communication we report that the vimentin-GFA transition in rat brain occurs during the 2nd-3rd week, ie, at the time of rapid myelination when dividing glioblasts in white matter differentiate into oligodendroglia and interfascicular astrocytes.

Alzheimer's disease: Tau proteins, the promoting factors of microtubule assembly, are major components of paired helical filaments

A rabbit antiserum was raised against paired helical filaments (PHF). This antiserum stains specifically neurofibrillary tangles (NFT) at the light-microscopic level and PHF at the electron-microscopic level in sections of Alzheimer neocortex and hippocampus. We studied the nature of the antigens recognized by this antiserum by immunocytochemistry, immunoblots and immunoadsorption. These approaches showed that the anti-PHF specifically labels a set of low molecular weight 65-50 kDa microtubule-associated proteins, named Tau proteins, which are promoting factors of microtubule assembly. Furthermore, antisera against Tau proteins stained NFT. It is concluded that neurofibrillary tangles are very likely composed of aggregated Tau proteins. This process might be due to an abnormal Tau protein synthesis or to an unknown lesion of certain pyramidal neurons leading to an aggregation of Tau proteins.

Demonstration of microglial cells in and around senile (neuritic) plaques in the Alzheimer brain. An immunohistochemical study using a novel monoclonal antibody

A monoclonal antibody, termed AD11/8, reactive to microglial cells, was produced by immunization of mice with partially purified amyloid fibrils of senile (neuritic) plaques. With immunoperoxidase staining on human tissues, AD11/8 also recognized macrophages in the red pulp of the spleen, Kupffer cells in the liver, and macrophages in the bone marrow. The results show that AD11/8 recognizes the antigens associated with mononuclear phagocytes lineage. In normal brains a few resting microglial cells were stained in gray matter, and less frequently in white matter. In senile dementia of the Alzheimer type numerous microglial cells were stained intensively and they often formed clusters in gray matter. By double immunostaining with AD11/8 and a polyclonal antibody against synthetic amyloid beta-protein, clustered microglial cells were observed in and around senile plaques with amyloid deposits. Some amyloid plaque cores were surrounded by microglial cell processes. These results indicate that microglial cells may play an important role in senile plaque formation.

Receptor for advanced glycation endproducts (RAGE) and the complications of diabetes

Receptor for Advanced Glycation Endproducts (RAGE) is a multiligand member of the immunoglobulin superfamily of cell surface molecules with a diverse repertoire of ligands. These ligands include products of nonenzymatic glycation, the Advanced Glycation Endproducts (AGEs, enriched in the diabetic milieu), members of the S100/calgranulin family of proinflammatory mediators, beta-sheet fibrillar structures (characteristic of amyloid) and amphoterin (present at high levels in the tumor bed). Ligation of RAGE by its ligands upregulates expression of the receptor and triggers an ascending spiral of cellular perturbation due to sustained RAGE-mediated cellular activation. For example, in the setting of diabetes, a vascular environment rich in AGEs and S100/calgranulins accelerates atherogenesis in murine models, and this can be blocked by intercepting the interaction of ligands with RAGE. While RAGE is certainly not the cause of diabetes, it functions as a progression factor driving cellular dysfunction underlying the development of diabetic complications as the microenvironment becomes enriched in its ligands. Though further studies will be required to determine the importance of RAGE-mediated cellular activation to human chronic diseases, it represents a novel receptor-ligand system potentially impacting on a range of pathophysiologic conditions.

Patterns of aberrant sprouting in Alzheimer's disease

Alzheimer's disease (AD) is characterized by extensive synaptic and neuronal loss and by plaque formation in the cortex, but the mechanisms responsible for synaptic plasticity in the neocortex are still not completely understood. To analyze the sprouting response in AD cortex, we compared the patterns of GAP-43 with synaptophysin immunoreactivity. In AD, GAP-43 immunohistochemistry revealed extensive sprouting in the hippocampal molecular layer, stratum polymorphous, CA1 region, and prosubiculum. These regions presented abundant anti-GAP-43-immunoreactive coiled fibers and dystrophic neurites in association with plaques. Some of these sprouting structures were colocalized with anti-synapto-physin- and anti-neurofilament-positive neurites. The AD neocortex was characterized by an overall decrease in GAP-43 immunoreactivity accompanied by sprouting neurites in the areas of synaptic pathology. We conclude that GAP-43 might be involved in the mechanisms of synaptic plasticity in the AD cortex, as well as in the process of aberrant sprouting in the neuritic plaques.

Up-regulation of mitogen-activated protein kinases ERK1/2 and MEK1/2 is associated with the progression of neurofibrillary degeneration in Alzheimer's disease

The abnormal hyperphosphorylation of tau in Alzheimer's disease (AD) has been proposed to involve the extracellular-signal-regulated protein kinase (ERK) of the mitogen-activated protein (MAP) kinase family. ERK is phosphorylated and thereby activated by MAP kinase kinase (MEK). In the present study, we determined the intracellular and regional distribution of the active forms of both MEK1/2 and ERK1/2, i.e. p-MEK1/2 and p-ERK1/2 in the entorhinal, hippocampal, and temporal cortices of 49 brains staged for neurofibrillary changes according to Braak and Braak's protocol. We found that p-MEK1/2 and p-ERK1/2 were present in the initial stages of neurofibrillary degeneration in the projecting neurons in the transentorhinal region, and extended into other brain regions co-incident with the progressive sequence of neurofibrillary changes up to and including Braak stage VI. It appeared that the accumulation of p-MEK1/2 and p-ERK1/2 was initiated in the cytoplasm of pretangle neurons in varying size granules, which grew into large aggregates co-existing with the progressive development of neurofibrillary tangles. Accumulation of p-MEK1/2 and p-ERK1/2 was found in cases with stages I-III neurofibrillary degeneration, which were devoid of amyloid deposition. These data provide direct in situ evidence consistent with the possible involvement of MAP kinase pathway in the hyperphosphorylation of tau and the presence of this lesion before deposition of beta-amyloid in AD.

Water diffusion in the giant axon of the squid: implications for diffusion-weighted MRI of the nervous system

To clarify the result that marked diffusional anisotropy had been found in nomyelinated nerve, and in completion of an evaluation of the role of all longitudinal axonal structures, we report NMR measurements of water diffusion in the giant axon of the squid, where diffusional anisotropy is determined by the neurofilamentary structure. The diffusion coefficients of water parallel and perpendicular to the long axis of the squid giant axon at 20 degrees C are (1.61 +/- 0.06) x 10(-5) cm2 s-1 and (1.33 +/- 0.09) x 10(-5) cm2 s-1, respectively, which yield an anisotropic diffusion ratio of 1.2 +/- 0.1. Water diffusion in the squid giant axon is therefore quite rapid and nearly isotropic, thus eliminating the possibility of a significant role for the longitudinally oriented neurofilaments in producing diffusional anisotropy within the axoplasm. In conjunction with our work on garfish nerves therefore, only membranes, either as numerous axonal membranes or as myelin (if present), remain to fulfill the role of the primary determinant of anisotropic water diffusion in nerve and in white matter.

NACP/alpha-synuclein immunoreactivity in fibrillary components of neuronal and oligodendroglial cytoplasmic inclusions in the pontine nuclei in multiple system atrophy

We examined neuronal cytoplasmic inclusions (NCIs) and oligodendrocytic glial cytoplasmic inclusions (GCIs) in the pontine nuclei in multiple system atrophy (MSA) using antibodies against the non-amyloid beta component of Alzheimer's disease amyloid precursor protein (NACP/alpha-synuclein). Our immunohistochemical study revealed that anti-NACP antibodies labeled both NCIs and GCIs. Immunoelectron microscopy showed that positive reaction products were localized on the 15- to 30-nm-thick filamentous components of NCIs and GCIs. The present study demonstrates that NACP is associated with cytoplasmic inclusions of MSA, and suggests a role of NACP in abnormal filament aggregation in neuronal degeneration.

Hyperphosphorylation of tau in PHF

Tau in PHF is known to be highly phosphorylated and immunochemical study has indicated the similarity of the phosphorylation between PHF-tau and fetal tau. We have determined the exact phosphorylation sites in both PHF-tau and fetal rat tau by ion-spray mass spectrometry and sequencing of ethanethiol-modified peptides. In PHF-tau, 19 sites have been identified; all the phosphorylation sites except for Ser-262 are localized to the amino- and carboxyl-terminal flanking regions of the microtubule-binding domain. Half of them are shared by fetal tau. Thus, PHF-tau is much more phosphorylated. Whereas most of the sites in fetal tau are proline-directed, half of them in PHF-tau are nonproline-directed. Overall, the hyperphosphorylation of PHF-tau can be considered to consist of fetal-type phosphorylation and additional proline-directed and nonproline-directed phosphorylation. This extraphosphorylation may provide PHF-tau with the unusual characteristics including assembly incompetence.

Alzheimer neurofibrillary degeneration: significance, etiopathogenesis, therapeutics and prevention

Alzheimer disease (AD) is multi-factorial and heterogeneous. Independent of the aetiology, this disease is characterized clinically by chronic and progressive dementia and histopathologically by neurofibrillary degeneration of abnormally hyperphosphorylated tau seen as intraneuronal neurofibrillary tangles, neuropil threads and dystrophic neurites, and by neuritic (senile) plaques of beta-amyloid. The neurofibrillary degeneration is apparently required for the clinical expression of AD, and in related tauopathies it leads to dementia in the absence of amyloid plaques. While normal tau promotes assembly and stabilizes microtubules, the abnormally hyperphosphorylated tau sequesters normal tau, MAP1 and MAP2, and disrupts microtubules. The abnormal hyperphosphorylation of tau also promotes its self-assembly into tangles of paired helical and or straight filaments. Tau is phosphorylated by a number of protein kinases. Glycogen synthase kinase-3 (GSK-3) and cyclin dependent protein kinase 5 (cdk5) are among the kinases most implicated in the abnormal hyperphosphorylation of tau. Among the phosphatases which regulate the phosphorylation of tau, protein phosphatase-2A (PP-2A), the activity of which is down-regulated in AD brain, is by far the major enzyme. The inhibition of abnormal hyperphosphorylation of tau is one of the most promising therapeutic targets for the development of disease modifying drugs. A great advantage of inhibiting neurofibrillary degeneration is that it can be monitored by evaluating the levels of total tau and tau phosphorylated at various known abnormally hyperphosphorylated sites in the cerebrospinal fluid of patients, obtained by lumbar puncture. There are at least five subgroups of AD, each is probably caused by a different etiopathogenic mechanism. The AD subgroup identification of patients can help increase the success of clinical trials and the development of specific and potent disease modifying drugs.

Aluminum and Alzheimer's disease

There is now substantial evidence indicating that an accumulation of aluminum occurs in grey matter in diseases associated with Alzheimer neurofibrillary degeneration. Four principle sites of aluminum accumulation have been identified in Alzheimer's disease: DNA containing structures of the nucleus, the protein moieties of neurofibrillary tangles, the amyloid cores of senile plaques and cerebral ferritin. Consideration of the extensive information now available on the toxic effects of aluminum in these four loci strengthens the hypothesis that aluminum could be important in the pathogenesis of this neurodegenerative process. The evidence, however, does not support an etiological role for aluminum in Alzheimer's disease. The primary pathogenic events responsible for Alzheimer's disease are presumed to have affected the genetically determined barriers to aluminum resulting in increased amounts of this toxic element to vulnerable target sites.

Inhibition of tau fibrillization by oleocanthal via reaction with the amino groups of tau

Tau is a microtubule-associated protein that promotes microtubule assembly and stability. In Alzheimer's disease and related tauopathies, tau fibrillizes and aggregates into neurofibrillary tangles. Recently, oleocanthal isolated from extra virgin olive oil was found to display non-steroidal anti-inflammatory activity similar to ibuprofen. As our unpublished data indicates an inhibitory effect of oleocanthal on amyloid beta peptide fibrillization, we reasoned that it might inhibit tau fibrillization as well. Herein, we demonstrate that oleocanthal abrogates fibrillization of tau by locking tau into the naturally unfolded state. Using PHF6 consisting of the amino acid residues VQIVYK, a hexapeptide within the third repeat of tau that is essential for fibrillization, we show that oleocanthal forms an adduct with the lysine via initial Schiff base formation. Structure and function studies demonstrate that the two aldehyde groups of oleocanthal are required for the inhibitory activity. These two aldehyde groups show certain specificity when titrated with free lysine and oleocanthal does not significantly affect the normal function of tau. These findings provide a potential scheme for the development of novel therapies for neurodegenerative tauopathies.